SU(2) instantons with boundary jumps and spin tunneling in magnetic molecules

Coherent state path integrals are shown in general to contain instantons with jumps at the boundaries, i.e., boundary points lying outside classical phase space. Inclusion of these instantons is shown to resolve the "missing quench paradox" in the magnetic molecule Fe8, i.e., the fact that the tunneling between the ground Zeeman states of this molecule is quenched at only four magnetic field values, instead of the ten that would be expected from the topological Berry phase between interfering instantons. An approximate formula is found for the location of the four remaining quenches.     

Mössbauer Study of Oxygenated Iron-Phthalocyanines,a Precursor of Magnetic Storage Material

⁵⁷Fe transmission Mössbauer spectroscopy and X-ray diffractometry were used to study - and -polymorphs of iron phthalocyanines (FePc) to get information about their oxygenation in connection with controlled pyrolysis of flat layered phthalocyanines initiated by radicals at relatively low temperatures, to form acicular carbide particles encaged in carbon. Mössbauer spectroscopy and XRD revealed that the oxygenation of both - and -polymorphs of FePc was successfully achieved. New Mössbauer spectral components (doublets) appeared upon the oxygenation in both and FePc. This can be attributed to iron microenvironments containing oxygen between the layers of iron phthalocyanines.     

Symmetrization of matrix technique in a finite element context

A finite element Galerkin-based formulation of the mass conservation and momentum equations can require, if convective type terms are retained in the coefficient matrix, a non-symmetric solver. The resulting increase in core storage for efficient utilization of CPU time can be considerable. The current paper advocates a simple symmetrization of matrix technique, at element level which results in a considerable reduction in core requirement. The increase in CPU time required when solving linear systems of equations is considerable. However, for nonlinear systems the penalty can be negligible.     

The polarography of oximes: I. 9,10-Phenanthraquinone monoxime

Polarography of 9,10-phenanthraquinone monoxime has been carried out in buffers (pH 3.50 to 13.40) of constant ionic strength 0.5 M in 40% alcoholic solutions at 35 ± 0.5 °C. The oxime group underwent diffusion-controlled reduction (4e) over the whole pH range studied. The number of electrons involved in the reduction was found coulometrically as well as by incorporating the value of the diffusion coefficient, obtained by using a McBain-Dawson cell, into the Ilkovic equation. Controlled potential electrolyses and uv spectroscopic methods were used to identify the products. Koutecky's method was used to compute the kinetic parameters (αn_aand ?log k_f,h^o) for the reduction of the oxime group and reduction mechanisms are proposed.     

Pseudohalide derivatives of (η -cyclopentadienyl-η-methylcyclopentadienyl) titanium (IV)

Summary Pseudohalide complexes of the (-cpL)TiXZ type (where cp = cyclopentadienyl, L = -McCs₅-H₄ and X = N3, NCS, NCO or NCSe) have been prepared in aqueous and nonaqueous media and characterized by elemental analyses, i.r. and n.m.r. spectroscopy. I.r. spectroscopy shows that NCS, NCO and NCSe are bonded to the titanium atom through nitrogen in these complexes which are thus true isothiocyanato, isocyanato and isoselenocyanato derivatives respectively.